1. Field of the Invention
The present invention relates generally to the detection of volatile and semi-volatile materials, and more particularly, to the use of insects to assist in the detection of volatile and semi-volatile materials, especially “sticky” volatile and semi-volatile chemicals that have a tendency to adhere to contacting surfaces, are present in low concentrations, and are commonly associated with certain types of explosives and narcotics.
2. Related Art
Volatile and semi-volatile chemicals may be detected in the field with portable instruments or in the laboratory with previously collected samples. Typically, these instruments use chromatographic separation (e.g., gas chromatography) to detect the volatile or semi-volatile chemical, but in some cases, these instruments may use ion mobility spectrometry.
There are also non-instrumental techniques available for the detection of volatile or semi-volatile chemicals. For example, indicator papers that change color are available for the detection of some analytes. However, the number of analytes detectable by this approach is very limited. Most non-instrumental detection methods are dominated by the use of trained mammalian systems (e.g., canines) that use their olfactory ability to report detection of a volatile or semi-volatile chemical. Canines have been used extensively for smuggling interdiction, explosives detection, search and rescue, etc.
As an alternative, the olfactory abilities of insects can be harnessed for use in detecting the presence of volatile or semi-volatile chemicals. This can be achieved by monitoring or observing an instinctual or trained behavior exhibited by the insect in response to sensing the presence of the volatile or semi-volatile chemical. In particular, honey bees, Apis mellifera, can be utilized for vapor detection of such chemicals by monitoring their Proboscis Extension Reflex (PER). Neurologists, psychologists, physiologists and others have utilized PER in bees as a model for examining learning and memory. Studies have shown that bees can be trained or conditioned to exhibit PER in response to sensing a specific volatile and semi-volatile chemical. (See, e.g., Abramson et al., Learning in the Africanized Honey Bee: Apis Mellifera L. Phys. & Behavior 62: p. 657-74 (1997); See also Bitterman et al., Classical Conditioning of Proboscis Extension in Honeybees Journal of Comp. Psychology 97: 107-19 (1983), the contents of both are hereby incorporated by reference).
In contrast to their mammalian counterparts, honey bees are much less expensive to raise, train and deploy, as well as being self renewing, relative to canines. A “handler” is not necessary for each and every honey bee. A trainer may be centrally located and capable of producing and deploying hundreds of sensors/conditioned honey bees daily.
Furthermore, observation of the trained PER behavior displayed by the insect in response to a specific vapor or odor can be facilitated by using instrumentation capable of monitoring such behavioral movements of the bees and recording, displaying, or communicating a positive test event to the user. Portable instruments that use insects to detect the presence of volatile or semi-volatile compounds have been developed. For instance, a patent issued to Davis et al. (U.S. Pat. No. 7,237,504, the contents of which are hereby incorporated by reference) describes a portable device that uses a camera to detect the PER response of bees in response to a volatile chemical of interest.
Commercial applications that use the olfactory abilities of honey bees vary widely and include transportation security, search and rescue, narcotics interdiction, medical diagnostics, food quality/control, facility security, and any other industry that would benefit from having the capability to qualitatively detect whether a volatile or semi-volatile is present in a product or item.
However, several problems and limitations exist with the current state of the art for apparatuses capable of harnessing the olfactory abilities of insects. For instance, one critical limitation with existing prototypes and products is that they are not designed to achieve detection of volatile chemicals at very low concentrations. This is especially important and challenging for certain types of “sticky” volatile and semi-volatile chemical vapors that are emitted from explosives and some types of narcotics since they tend to adhere to contacting surfaces, thus lowering their effective concentration in a sample of air even further (typically at low ppt). (See, e.g., Gowadia, H. A. and Settles, G. S., The natural sampling of airborne trace signals from explosives concealed upon the human body. Journal of Forensic Sciences 46(6), (2001), the contents of which are hereby incorporated by reference.)
The Davis patent (U.S. Pat. No. 7,237,504) as well as existing prototypes and products for bee sensing apparatuses all utilize extensive ducting means that comprise tubes, valves, and branches to deliver individual streams of air to each individual insect. This arrangement greatly increases the amount of surface area within the instrument that comes in contact with the air sample to be tested prior to presentation to the insects for detection. As a result, the ability of these existing devices to detect “sticky” volatile and semi-volatile chemicals present in a sample at low concentrations is limited.
Therefore, a need exists in the art for an improved portable device or apparatus that is capable of harnessing the sensing abilities of insects in a way that allows detection of volatile and semi-volatile chemicals present in a sample at low concentrations and that overcomes the tendency of some of these vapors to stick to contacting surfaces.